Isotopic effect in the radiolysis of water. Diffusion-kinetic modelling up to 300°C

Diffusion-kinetic calculations [1-3] have been analysed to determine the isotopic effect in the radiolysis of water with ionising radiation of linear energy transfer characteristics (LET) from 0.2 to 60 eV/nm and at temperatures up to 300°C. This analysis shows that, for low LET radiation, the spur decay of e^- _aq is slower in D₂O and results in a higher yield of e^- _aq, g(e^- _aq), at 10^-7 -10^-6s after the ionisation event. In low LET radiolysis, g(OD) ≈ g(OH) over the whole range of temperature but in high LET radiolysis g(OD) is clearly lower than g(OH). The isotopic effect on the yields of the radical products is enhanced by increasing LET but diminished by increasing temperature. The yields of the molecular products show the opposite isotopic effect to their radical precursors, namely g(D₂) is 10-20% lower than g(H₂) and g(D₂O₂) > g(H₂O₂). A particularly significant difference between g(D₂O₂) and g(H₂O₂) has been found at LET = 20 eV/nm. The isotopic dependence of the g-values estimated for fast neutron radiolysis is also presented.     

Photolysis of water-carbon tetrachloride and water-chlorobenzene saturated solutions and their two-phase systems. Quantum yields of chloride ions

The quantum yields of formation of chloride ions were determined in photolysis (=254 nm) of watercarbon tetrachloride organic phase of CCl₄(Cl^–)=0.89±0.04 water-chlorobenzene (_PhCl(Cl^–)=0.137± ±0.005) two-phase systems and saturated aqueous solutions of carbon tetrachloride (_CCl4(Cl^–)=18.9±5.6 and chlorobenzene _PhCl(Cl^–)=0.56±0.03. The quantum yields of chloride ions obtained from these systems are compared with partial radiation yields in the same systems. A mechanism for formation of Cl^– ions is proposed.     

Radiolytic synthesis of Rh2(CO)4Cl2 and Rh6(CO)16 from RhCl3 in ethanol under CO atmosphere

Ethanolic solutions of Rh^III chloride exposed to γ-radiation under CO atmosphere are shown to be totally reduced into Rh^I complexes (Rh₂(CO)₄Cl₂ and Rh(CO)₂Cl^-₂) within a few hours with a radiolytic reduction yield of about 6.0 elementary reductions/100 eV (6.2·10^-7 mol·J^-1). The chloride ions freed in the medium inhibit further reduction through Rh(CO)₂Cl^-₂ formation. On addition of copper metal under the same conditions, Rh^III is transformed into Rh₆(CO)₁₆ with a conversion yield 50%. This cluster is formed via Rh₂(CO)₄Cl₂ although Rh(CO)₂Cl^-₂ is also present under these conditions. Rh₆(CO)₁₆ cluster is also formed under radiolysis by direct reduction of Rh₂(CO)₄Cl₂, but metallic rhodium and other reduced products are obtained at the same time.     

Free radical inactivation of trypsin

Reactivities of free radical oxidants, ^.OH, Br^-·₂ and Cl₃COO^. and a reductant, CO^-·₂, with trypsin and reactive protein components were determined by pulse radiolysis of aqueous solutions at pH 7, 20°C. Highly reactive free radicals, ^.OH, Br^-·₂ and CO^-·₂, react with trypsin at diffusion controlled rates, k(^.OH + trypsin) = 8.2 × 10¹⁰ M^-1 s^-1, k(Br^-·₂ + trypsin) = 2.55 × 10⁹ M^-1 s^-1 and k(CO^-·₂ + trypsin) = 2.6 × 10⁹ M^-1 s^-1. Moderately reactive trichloroperoxy radical, k(Cl₃COO^. + trypsin) = 3 × 10⁸ M^-1 s^-1, preferentially oxidizes histidine residues. The efficiency of inactivation of trypsin by free radicals is inversely proportional to their reactivity. The yields of inactivation of trypsin by ^.OH, Br^-·₂ and CO^-·₂ are low, G(inactivation) = 0.6-0.8, which corresponds to ∾ 10% of the initially produced radicals. In contrast, Cl₃COO^. inactivates trypsin with ∾ 50% efficiency, i.e. G(inactivation) = 3.2.     

A study of the radiation-chemical transformation of n-hexane on the surface of aluminum

The radiation-chemical decomposition of n-hexane in the Al-n-hexane system under the action of gamma radiation was studied by reflectance-absorption IR spectroscopy. The radiolysis of n-hexane on the surface of aluminum at absorbed doses of 5 kGy ≤ D _γ ≤ 40 kGy was accompanied by the formation of aluminum alkyls, π-complexes of olefins, and aluminum hydrides. The kinetics of the accumulation of molecular hydrogen was analyzed to determine its radiation-chemical yield, G _ads (H₂) = 29.6 molecules/100 eV. A possible mechanism of this process is discussed.     

Radiation-chemical yield of excited neodymium(III) in laser liquids POCl<Subscript>3</Subscript>-MCl<Subscript>n</Subscript>-<Superscript>235</Superscript>UO<Subscript>2</Subscript><Superscript>2+</Superscript>-Nd<Superscript>3+</Superscript> (M = Ti,Zr, Sn,or Sb)

Results of measurements of the yield of Nd³⁺ radioluminescence photons in inorganic laser liquids POCl₃-MCl_n-²³⁵UO ₂ ²⁺ -Nd³⁺ (M = Ti, Zr, Sn, or Sb) during homogeneous excitation by uranium α-particles are presented. It was found that the intensity of radioluminescence corresponding to the ⁴ F _3/2 → ⁴ I _11/2 transition in neodymium ions depends on the solvent composition. Data on the radiation-chemical yield, G, of excited neodymium ions in the POCl₃-MCl_n-²³⁵UO ₂ ²⁺ -Nd³⁺ (M = Ti, Zr, Sn, or Sb) system were obtained. At a neodymium concentration of 0.25 mol/l, the values of G for the excited ions were 0.60 ± 0.10, 0.84 ± 0.10, 1.20 ± 0.10, and 1.64 ± 0.16 ion/100 eV in solutions with TiCl₄, ZrCl₄, SnCl₄, and SbCl₅, respectively. The maximum yields of excited ions estimated at G = 1.68 ± 0.10 and 2.20 ± 0.24 ion/100 eV were obtained for the solutions with SnCl₄ and SbCl₅, respectively, at neodymium ion concentrations above 0.4 mol/l.     

The mechanism for diamagnetic products formation under the radiolysis of alkali nitrates

Based on optical measurements, the kinetics of peroxynitrite accumulation in alkali nitrate crystals γ-irradiated at 310 K has been investigated. The initial radiation chemical yields were calculated to be 0.60±0.05, 0.14±0.03, 0.35±0.03, 0.65±0.04 (100 eV)⁻¹ for NaNO₃, KNO₃, RbNO₃, and CsNO₃, respectively. The mechanism for the radiolysis of crystalline alkali nitrates is interpreted in terms of formation of the peroxynitrite ions and the nitrite ions from high-energy singlet and triplet excited states of the nitrate ions, respectively. These states can be generating under the radiationless transitions of electrons from the cation conductivity band into the anion conductivity band accompanied by the Auger excitation of the nitrate ions.     

Determination of radiation yields of ionogenic products of two-phase water-dibutylphosphate systems by capillary isotachophoresis

The main ionogenic radiolytical degradation products are monobutylphosphate, phosphoric acid, formic, acetic, propionic and butyric acids as the result of gamma-irradiation of two-phase water-dibutylphosphate system. The products were determined using capillary isotachophoresis. According two-phase theory the total (_T G(X)) and partial (G_I(X) for aqueous phase and G_II(X) for organic phase) radiation yields of products and decomposition of DBP in the radiolysis of two phase water-dibutylphosphate systems were calculated from the results.Dedicated to 65th birthday of prof. L. T. Bugaenko     

Free Ḃr atom and free radical reactions in the radiolysis of 1,2-dibromoethane (DBE) and other bromohydrocarbons in air-free aqueous solutions

G(Br^-)-values have been evaluated in Ar- and N₂O-saturated 1,2-dibromoethane (DBE), bromobutane, propylbromide and bromopentane (BP) under a variety of experimental conditions in aqueous solutions. G(Br^-) increases with increasing halogenated hydrocarbon concentration and with increasing pH. Free Ḃr atoms formed as a result of e^-_aq and ȮH radical reactions with bromohydrocarbons are considered to initiate a chain reaction. Another chain reaction has been invoked to explain the high G(Br^-) at high pH. Ḃr radicals may form a reactive intermediate with OH^- (BrOH^⨪), which decays to Br^- and ȮH. The ȮH radicals have been found to interact with bromohydrocarbons and eventually yields Br^- ions. The formation of Br^- ions is accelerated both at acidic and alkaline pH in systems containing t-butanol. Dose rate studies in Ar- and N₂O-saturated 1,2-DBE and BP show an increase in G(Br^-)-values at low dose rate and confirm the occurrence of a chain reaction initiated by Ḃr atoms. From these studies the rate constant for the reaction of Ḃr with 1,2-DBE has been calculated to be ∼ 1 × 10⁶M^-1s^-1.     

Quantum-chemical simulation of interaction of polycaproamide with a lithium chloride solution in dimethylacetamide

Quantum-chemical calculations of interaction between lithium chloride and dimethylacetamide (DMAc) and between the polycaproamide model fragment CH₃NHCO(CH₂)₅NHCOCH₃ and a lithium chloride solution in DMAc were performed. The software package GAMESS with the MINI basis set was used in the calculations. Models of the solution included 2 LiCl molecules and 8–16 DMAc molecules. All of these models suggest three potential energy minimums corresponding to three stable structures that differ in the relative arrangement of lithium and chloride ions. A decrease in the amount of solvent in the system leads to transition from Li⁺(DMAc)₄Cl^- to Li⁺...Cl^-(DMAc)₃ and then to the (LiCl)₂(DMAc)₂ species, which crystallizes to form the 1: 1 crystal solvate. The mechanism of dissolution of polycaproamide in DMAc containing lithium chloride was refined.     

Radiolysis of the trichloromethane-water two-phase system

The radiolysis of the CHCl₃-water two-phase system in the absence of oxygen has been investigated by continuous -ray irradiation. The major products of radiolysis were determined to be the same, except for tetrachloromethane, as in the case of the radiolysis of pure CHCl₃, however, the radiolytical yields were different. The dependencies of gross radiation yields of the radiolysis products on the CHCl₃ volume fraction follow the two-phase rule of additivity. The partial yields of all products determined were calculated for both phases and revealed that the major products HCl and C₂H₂Cl₄ are formed in both phases. The other organic products are formed mainly in the organic phase. The decrease of organic product yields is probably caused by the presence of water in the organic phase. The radiolysis of CHCl₃-water did not proceed in the diffusional regime even at high absorbed doses due to the relatively high solubility of CHCl₃ in water andvice versa.     

Chemical effects of low energy electron impact on hydrocarbons in the gas phase: III. Cyclopropane

The simulated radiolysis of cyclopropane with low energy electrons (3.5 to 15.0 eV) was investigated. The setup used for the irradiations has been described previously. Appearance curves of the various products formed under electron impact were determined. The features observed on these curves yield various indications.(1) Some products arise from the dissociation of excited molecules. Contributing states are the following ones: a triplet state at 7.4 eV, singlet states at 6.7 and/or 7.7 eV, at 8.55 eV, at 9.4 and/or 9.95 eV and superexcited states lying around 10.2 eV. As in other hydrocarbons studied, the electron impact excitation cross section shows a steep increase at the ionization potential. (2) Other products result from ion fragmentation and ion—molecule reactions.A reaction scheme was proposed to account for the chemical effects associated with excited states and the yields of excited molecules in dissociating states were derived from experimental data. The observations relative to excited molecule fragmentation are in conformity with photolysis data. Additional information on the decomposition processes of molecules excited in the triplet state at 7.4 eV, in the singlet states at 6.7 and/or 7.7 eV and in the superexcited states were obtained.Owing to the complexity of ionic mechanisms it was not possible to distinguish between the contributions of ionization and excitation. Only the radiation chemical yield of products, G(products), was evaluated. The values found for G(products) just above the ionization potential are close to the data obtained in conventional radiolysis which could indicate that secondary electrons having such energies play an important role in radiation chemistry.     

The radiolysis of bromophenol blue in aqueous solutions

The effect of gamma radiation on the color intensity of aerated and oxygenated aqueous solution of bromophenol blue (BPB) was investigated. Ionizing radiation at increasing absorbed doses (D) brought about gradual bleaching (i.e. decrease in optical absorbance, -ΔA) of bromophenol blue solutions. The molar extinction coefficients of acidic, neutral, and alkaline solutions were measured and found to be independent of temperature during spectrophotometry between 20 and 40°C. Aerated and oxygen-saturated acidic solutions showed a linear response -ΔA vs D) up to doses of 2.4 and 2.1 kGy, respectively. Aerated alkaline solutions on the other hand showed a linear response up to 4.8 kGy. The decoloration yields for 5 × 10^-5 M bromophenol blue aqueous solutions, G(-BPB), obtained from the decrease in absorbance at 591 nm wavelength for acidic, neutral, and alkaline solutions, were 0.244, 0.113, and 0.098 (100 eV)^-1, respectively. The first-order rate constant for the reaction of OH radical with bromophenol, obtained from competition reactions with ethanol at pH 4, was found to be 9.1 +- 1.2 × 10⁹ M^-1 s^-1. The degree of decoloration of bromophenol blue in acidic solutions was found to decrease upon the addition of ethanol, G(-BPB) decreasing from 0.24 to 0.088 upon the addition of ethanol at a concentration of 10^-2M. Suggestions are made for possible radiation dosimetry in the dose range (0.1–5 kGy) by means of spectrophotometric analysis of absorption spectra.     

Radiolysis and corrosion of238Pu-doped UO2 pellets in chloride brine

Deaerated 5 M NaCl solution is irradiated in the presence of UO₂ pellets with α-radiation from²³⁸Pu. Experiments are conducted with²³⁸Pu doped pellets and others with²³⁸Pu dissolved in the brine. The radiolysis products and yields of mobilized U and Pu from the oxidative dissolution of UO₂ are determined. Results found for radiolysis products and for the oxidation/dissolution of pellets immersed in Pu containing brine are similar to results for Pu doped pellets, where the radiation chemical processes occur only in the liquid layer of some 10 σm thickness adjacent to the pellet. The yield of radiolysis products is comparable to earlier results, that of mobilized U from the pellets is < 1% of the total amount of oxidized species. Thus, the radiation chemical yield (G-value) for mobilized hexavalent U is < 0.01 ions/100 eV. In spite of the low radiation yield for the corrosion, the rate of UO₂dissolution is higher than expected for the concentrations of long-lived oxidizing radiolysis compounds found in the solutions.     

Yttrium and Rare Earth Element Complexation by Chloride Ions at 25°C

Formation constants for yttrium and rare earth element (YREE) chloride complexation have been measured at 25°C by examining the influence of medium (NaClO₄ and NaCl) on YREE complexation by fluoride ions and methyliminodiacetate (MIDA). YREE chloride complexation constants _Clβ₁(M) obtained in this work using dissimilar procedures are in good agreement and indicate that, at constant temperature and ionic strength, _Clβ₁(M) does not vary significantly across the fifteen-member series of elements. The ionic strength μ dependence of YREE chloride formation constants between 0 and 6 molar ionic strength can be written, for all YREE, as ${\text{log}}_{{\text{CI}}} \beta _1 \left( M \right) = \log _{{\text{CI}}} \beta _1^0 \left( M \right) - 3.066\mu ^{0.5} /\left( {1 + 1.727\mu ^{0.5} } \right)$ where _Clβ₁(M) = [MCl²⁺][M³⁺]^?1[Cl^?1]^?1 and log_Clβ₁ ^o(M) represents the MCl²⁺ formation constant for all YREE at zero ionic strength: log_Clβ₁ ^o = 0.65 ± 0.05.     

The radiation chemistry of iodophenolsThe research described herein was supported in part by the Office of Basic Energy Sciences of the Department of Energy. This is contribution No. NDRL 4019 from the Notre Dame Radiation Laboratory.

The technique of pulsed electron radiolysis has been used to determine absolute rate constants for the reaction of the hydrated electron, hydroxyl radical and hydrogen atom with ortho-, meta- and para-iodophenol in aqueous solution. These rate constants have been used to establish individual G-values for iodide production in the steady-state radiolysis of 2-iodophenol in a variety of radical scavenger-additive systems. For 2-iodophenol, specific efficiencies for e_(aq)⁻,  OH and  H reaction were determined as 0.89±0.03, 0.27±0.03, and 0.97±0.07, respectively. These data are compared to the available literature results for other halophenols.     

Investigation of radiochemical conversions in extraction systems based on tributyl phosphate

The use of halogenated organic compounds under the effect of ionizing radiation requires a comprehensive knowledge of their radiation stability. There is little experimental evidence on the radiolysis of fluorine-containing organic compounds in the literature, while a theoretical generalization enabling one to predict the main radiolysis pathways is completely lacking. This paper is concerned with the identification of stable radiolysis products of trichloromethyl-1,1,2-trifluoro-2,2-dichloroethyl ether (C₃F₃Cl₅ O), γ-irradiated separately and the extraction system based on tributyl phosphate. Practically all the C₃F₃Cl₅O radiolysis products were identified with the aid of gas-liquid chromatography, GC-MS, IR, UV and NMR spectroscopy and elemental analysis. Upon C₃F₃Cl₅O radiolysis, the formation of CCl₄, Cl₂, COCl₂, C₂ Cl₆, freons of various composition and long-chained ethers like CFCl₂−CF₂−O−CCl₂−CCl₃ takes place. The identification of radiolysis products allows to draw well-founded conclusions on the mechanism of C₃F₃Cl₅O radiolysis, representing a wide class of chlorine- and fluorine-containing organic compounds.     

Observation of hydrated electron, (SCN)2 .- and CO3 .- radical in high temperature and supercritical water

Transient radicals (hydrated electron, (SCN)₂ ^.- and CO₃ ^.-) formed in supercritical water have been observed by the pulse radiolysis technique. The change of spectra of these radicals with temperature has been measured. It was found that the spectra and absorption coefficients of the radicals, e^- _aq and (SCN)₂ ^.-, are strongly dependent on the temperature of the water. Since it was found that the absorption spectrum and molar absorption coefficient of CO₃ ^.- radical seem to be almost independent of temperature, G-values of OH and e^- _aq could be derived. Then, the absolute values of the absorption coefficients for the radicals could be calculated. The G-values of the radical products in water radiolysis tend to increase with increasing temperature up to 400°C. Based on the above observation, radiolysis of supercritical water is discussed.     

Radiation-chemical processes as disclosure of electronic states in a bis(dinitrogen) molybdenum complex

On the basis of experimental data the energy levels of the central-atom orbitals in the complex [Mo(N₂)₂(dppe)₂] [dppe = 1,2-bis(diphenylphosphine)ethane] were calculated. Using the diagram thus obtained the eletronic configuration of the irradiation-generated ion, [Mo(N₂)₂(dppe)₂]⁻, was determined to be as follows: (b_2g)² (e_g)⁴ (b_1g)¹ or (b_2g)² (e_g)⁴ (e_u). The yields from the decomposition of [Mo(N₂)₂(dppe)₂] in the solid phase in a hydrogen atmosphere were determined on the basis of the decrease in band intensities at 306 and 377 nm: G(− MoN₂)_306nm = 0.01, and G(− MoP)_377nm = 0.1 (molecules per 100 eV). In toluene solution it was found that G(− MoN₂) > G(− MoP). The yields observed were in accordance with the calculated levels. Using a mass spectrometer the volatile products of [Mo(N₂)₂(dppe)₂] radiolysis in H₂ and O₂ atmospheres were identified as H₃N, H₄N₂, NO and N₂O. In the light of the results mentioned above (as well as the IR results) a mechanism for the radiolysis of [Mo(N₂)₂(dppe)₂] in the solid phase was proposed.     

Radiolysis of chitosan

The γ-radiolysis of solid chitosan was studied. The radiolysis products hydrogen and ammonia were determined by chromatography and spectrophotometry (with Nessler’s reagent), respectively, and the amino groups were determined by potentiometic titration. The radiation-chemical yields were found to be G _{H 2} = 2.0 ± 0.3; G _{NH 3} = 5.8 ± 0.4 and G _{−NH 2} = 2.9 ± 0.8. The molecular mass of chitosan decreases with an increase in the absorbed radiation dose because of its degradation (G _D = 3.6 ± 0.4). A long-term posteffect was observed after irradiation. This is a preliminary report on the study concerning the search for optimal conditions of the synthesis of membranes from modified chitosan for removal of cadmium ions.